Types of airships
There are three types of airships:
Non-rigid airships (blimps)
This is the oldest and most simple type of construction. The airship´s envelope is filled with lifting gas and is kept at a pressure level in excess of the surrounding air pressure by one or several air filled ballonets. The airship only retains its shape due to the pressure of the lifting gas. The pressure must always be high enough to regulate all kinds of forces occurring during different flight maneuvers, for example air resistance at full speed. The gondola with engines, fuel tanks etc. is attached with suspension cables to the catenary curtain which is fixed to the top of the envelope. Due to the fact that the engines are mounted directly to the gondola, passengers are affected by engine noise and vibration.
1. Nose cone with battens 2. Forward ballonet 3. Gondola suspension 4. Aft ballonet 5. Rudder 6. Gondola 7. Engines 8. Lighting 9. Air vents 10. Air valves 11. Helium Valve Fig. Blimp by Goodyear/USA
This type of airship was specially developed for military purposes during World War II by GOODYEAR/USA and is now mainly used for advertising purposes.
Thanks to Graf von Zeppelin and his followers this type of airship achieved a design which is still admired to this day. Rigid airships retain their shapes by using an internal framework or a rigid outer skin. The lift gas cells lie underneath the framework and are mostly non-bulging. Air pressure fluctuations and different temperatures lead to changes to the filling levels of the gas cells. Rigid airships can be built very large. LZ 129 HINDENBURG and LZ 130 GRAF ZEPPELIN had a volume of 200,000 m3 and length of 245 m.
The benefits of rigid type of airship are:
- loads can be spread efficiently inside the envelope
- air stream and solar radiation have no direct effect on lift gas cells
- a leak in the envelope or a lift gas cell does not lead to loss of gas and consequently to nonmaneuverability
However, this type of airship is very costly and the dead load to payload ratio is comparatively higher than in non-rigid airships.
In order to combine the benefits of the two types of airships mentioned above, so-called semi-rigid airships were designed. The most popular semi-rigid airships were built by the Italian general and airship pioneer Umberto Nobile, who flew over the north pole in the airship NORGE in 1926. The semi-rigid airship maintains its envelope shape through ballonets and has a fixed keel to which various loads such as engines etc. are mounted.
Fig. Semi-rigid airship ITALIA (System Nobile)